Compaction of particulate matter

ABSTRACT

AN APPARATUS AND METHOD FOR COMPRESSING PARTICULATE MATERIAL USING AT LEAST ONE DIE IN A MOLD WHEREIN AT LEAST ONE ACTUATOR IS EMPLOYED FOR FORCING THE DIE TOWARD AND AWAY FROM THE MOLD AND AT LEAST ONE SERVO VALVE IS EMPLOYED FOR CONTROLLING THE ACTUATOR SO AS TO APPLY THE DIE BOTH STATIC AND DYNAMIC FORCES.

Oct. 19, 1971 w WALLACE ET AL 3,613,166

COMPACTION OF PARTICULATE MATTER Filed June 26, 1969 INVENTORS RICHARDW. WALLACE STANLEY R. PAVLICA mu M/MM ATTORNEY United States Patent3,613,166 COMPACTION 0F PARTICULATE MATTER Richard W. Wallace,Pittsburgh, and Stanley R. Pavlica, Irwin, Pa., assignors to DresserIndustries, Inc., Dallas,

Tex.

Filed June 26, 1969, Ser. No. 836,810 Int. Cl. A22b /08 US. Cl. 18-16.53 Claims ABSTRACT OF THE DISCLOSURE An apparatus and method forcompressing particulate material using at least one die in a moldwherein at least one actuator is employed for forcing the die toward andaway from the mold and at least one servo valve is employed forcontrolling the actuator so as to apply to the die both static anddynamic forces.

BACKGROUND OF THE INVENTION Heretofore there have been two primaryapproaches for improving procedures for the preparation of unitaryarticles from a plurality of particles. One approach has been throughthe chemistry and/or mineralogy of the particles while the otherapproach has been through increased densification of the unitaryarticle.

In the densification approach, larger and larger static forces have beenused to achieve a greater density of packing of the particles in thefinal article through sheer brute force.

Compaction progresses from an initial particle accomrnodation stagethrough an elastic and/or plastic deformation of the particles stage toa final stage where further compaction is achieved only by fracturingthe particles. Even with extremely large static forces, the individualparticles strongly resist plastic and/or fracture compaction so thatthere is a limit on the density of packing of particles by static forcealone.

Although static forces are very useful in compacting particles, the useof massive force alone to push the particles into a position of closestapproach with one another and therefore greatest densification is notthe best approach.

SUMMARY OF THE INVENTION According to this invention greaterdensification is achieved with lower static compaction forces byrestructuring the particle mass into a position of closest approach forthe particles by superimposing on the static force of compaction acyclical force of compaction. In this manner high densities in the finalunitary product are obtained without the necessity of very large staticforces. This results in a great savings in the size of the compactionapparatus employed and therefore in the cost of building, operating, andmaintaining such apparatus.

Accordingly, this invention relates to apparatus for compressingparticulate material in a mold cavity with at least one die using atleast one actuator means for forcing at least one die toward and awayfrom the cavity and at least one servo valve means operably connected toeach actuator to cause the actuator to apply to the die both a staticforce toward the cavity and a cyclical reciprocating, dynamic) forcetoward and away from the cavity.

Also according to this invention there is provided a method forcompacting particulate material by imposing at least one staticcompressive force on said material and superimposing on said staticforce at least one additional force 'which is cyclically applied withand against said static force in the range of from about 0.2 to about7000 cycles per second.

This invention is useful in the preparation of any unitary body from anysolid or solid-like particulate material. For example, this invention isuseful in the preparation of refractory shapes such as bricks from anyknown refractory material. This invention is also applicable to theformation of metallic parts from metal or metallic particles by generalprinciples well known in the field of powder metallurgy.

Accordingly, it is an object of this invention to provide new andimproved compaction apparatus. It is another object to provide a new andimproved compaction method. It is another object to provide a new andimproved method and apparatus for increasing the attainable density of aproduct formed from particulate material without also requiringincreased high static compaction forces. It is another object to providea new and improved method and apparatus for restructuring a mass ofparticles into positions of closest approach for the particles inrelation to each other while compacting the composite of particles intoa unitary product.

Other aspects, objects, and advantages of the invention will be apparentto those skilled in the art from the disclosure and the appended claims.

DETAIL-ED DESCRIPTION OF THE INVENTION The drawing shows a systememploying one embodiment of this invention.

More specifically, the drawing shows a base 1 fixedly holding upright,spaced-apart support members 2. Members 2 carry horizontal supportmember 3 which in turn carries an upper hydraulic cylinder 4. Upperpiston 5 of cylinder 4 is connected to upper crosshead 6 which isslidable on supports 2.

Base 1 carries a lower hydraulic cylinder 7 which contains lower piston8. Piston 8 supports lower crosshead 9 which is also slidably carried onsupports 2.

Mold 10 is supported by mold crosshead 11 which can also be slidablycarried on supports 2.

Thus, crossheads 6 and 9 are vertically movable by means of the pistons5 and 8 attached thereto while crosshead 11 can be vertically movablebut by manual or other means not shown.

Mold 10 has a vertical passage therethrough which defines mold cavity12.

Crosshead 9 has a lower die 13 attached thereto.

Crosshead 6 has an actuator means 14 attached thereto which actuatorcarries upper die 15.

Attached to actuator 14 are servo valve means 16 and 17.

As shown in the drawing, dies 13 and 15 are aligned with mold cavity 12so that the dies can be moved into and out from that cavity by operationof pistons 5 and 8.

Actuator 14 comprises a body 20 having a first, lower piston chamber 21therein which opens directly into an upper, second piston chamber 22which is of smaller, cross-sectional area taken in a horizontal planethan the cross-sectional area of first chamber 21. Body 20 has anopening 23 in the lowest side thereof adjacent mold 10 which is of ahorizontal cross-sectional area less than the horizontal cross-sectionalarea of first chamber 21.

Opening 23 allows a lower, first piston 25 to pass therethrough in adynamically sealing engagement. Piston 25 extends into the interior ofchamber 21 and extends downwardly outside of body 20 to carry die 15fixedly attached thereto.

Piston 25 carries an annular flange 26 on a portion thereof (a topportion thereof being shown in the drawing) in the interior of chamber21. Flange 26 extends out to the interior walls 27 for dynamic sealingtherewith thereby dividing chamber 21 into upper and lower subchambers28 and 29, respectively.

First piston 25 carries second piston 30 which mates with second chamber22 in a dynamically sealing relation.

Conduit 31 in body 20 openly connects sub-chamber 28 with servo valve 16while conduits 32 and 33 in body 20 openly connect second chamber 22 andlower cham ber 29, respectively, with servo valve 17.

Servo valves 16 and 17 can be any convention, high response servo valvewhich can be electrically actuated and which hydraulically operates byway of conduits 31 through 33 the pistons in the actuator. Such servovalves are commercially available and are well known in the art. Forexample, two applicable servo valves are fully and completely disclosedin Fluid Power International, volume 29, No. 334, January 1964, pages6-9, the disclosure of which is incorporated herein by reference. Aparticularly suitable servo valve is a conventional valve which employsan electromagnetic (electrodynamic) driver for receiving the electricalsignal and which also uses a pilot stage containing a pilot spool and apower stage containing a power spool. In such a device an electricsignal to the electrodynamic driver moves the vertically aligned pilotspool to allow oil under pressure to one of the two ends of the powerspool thereby shifting the power spool and allowing oil under pressureto leave the power stage and enter one of the chambers 22, 28, and 29 ofactuator 14 and apply a force to one of pistons 30 or 25 in a directioneither toward or away from mold cavity 12. The electric signals to theservo valve can be varied and reversed to cause the pilot and powerspools to oscillate back and forth thereby causing pressurized oil to beadmitted to the actuator in a cyclic fashion to cause reciprocation ofpiston 25 and, therefore, reciprocation of die 15.

In operation, crosshead 9 is raised by piston 8 until die 13 extendspartially into cavity 12. A group of particles are charged into cavity12 and come to rest on die 13.

Crosshead 6 is then lowered by piston until die 15 extends into theinterior of cavity 12 just contacting the upper level of the particlecomposite resting in the cavity.

An electric signal such as from a conventional oscillator is applied toservo valve 16 by way of electrical conductor 35 which causes oil orother non-compressible liquid to pass from a pressurized sourcerepresented by arrow 36 through conduit 31 into upper chamber 28 therebyforcing piston 25 downwardly against the particle composite in thecavity and thereby applying a static force to that composite. Liquid isremoved from the actuator and servo valve to its source by way of a linerepresented by arrow 36' when the process is completed.

An electrical signal is also supplied to servo valve 17 by way ofelectrical conductor 37 to admit pressurized liquid from its source,represented by arrow 38, through servo valve 17 and conduit 32 intochamber 22. This superimposes an additional force on piston 30 which istransmitted through piston 25 to die 15 and finally to the particlecomposite in cavity 12. By reversal of the signal in conductor 37, theflow of pressurized liquid through servo valve 17 is switched fromconduit 32 to conduit 33 thereby employing through chamber 29 an upwardforce on piston 25 and causing a reduction in the downward force onpiston 25 and die 15 thereby partially relieving the compacting pressureon the particle composite in cavity 12. By rapidly reversing theelectric signals in conduit 37 the pressurized liquid and the lowpressure return line, represented by arrow 38', are cyclically switchedfrom chamber 22 to chamber 29 and back thereby causing a reciprocatingor dynamic force to be applied through piston 25 and die 15 onto theparticle composite in cavity 12. This reciprocating force issuperimposed on the static force that is maintained by servo valve 16.

The static pressure applied to the particle composite can be anypressure up to 40,000, preferably about 7,000, pounds per square inch ofdie surface in contact with the particle composite. The reciprocatingforce controlled by 4 servo valve 17 can apply any additional pressureacting towards or away from cavity 12 up to 2,000, preferably 1,000,pounds per square inch of die area in contact with the particlecomposite. The cycling of the reciprocating force can vary from about0.2 to about 7,000 cycles per second.

The static and cycling forces can be applied to the particle compositein any sequence. For example, the static force can be applied to thecomposite first followed by the cycling force or the cycling force canbe applied first followed by the static force, or both forces can beapplied at substantially the same time. The common element of thisapplication of forces is that a static force with a superimposed cyclingforce are both applied to the particle composite over a finite period oftime. The cycling force restructures the particles in the composite topositions of closest approach to adjacent particles and, therefore, actsas a mechanical lubricant, while the static force continually urges theparticles together during the restructuring process.

As a further example in the operation of the apparatus of the drawing,assume a static force equivalent to 7,000 p.s.i. is applied throughservo valve 16 on the particle composite in cavity 12. Thereafter, acycling force equivalent to 1,000 p.s.i. is employed through servo valve17. When the cycling force is applied through conduit 32 in chamber 22it provides an additional 1,000 p.s.i. pressure to the 7,000 p.s.i.static pressure thereby providing a composite downward force equivalentto 8,000 p.s.i. When the cycling force is switched from conduit 32 toconduit 33, this force acts upwardly on flange 26 thereby reducing thetotal force acting downwardly to a magnitude equivalent to 6,000 p.s.i.Thus, in this example, at least 6,000 p.s.i. is always applied to theparticle composite while a cycling force is imposed on this static forcethereby raising the force equivalent acting on the composite from thestatic 6,000 p.s.i. up to 8,000 p.s.i. and back down to 6,000 p.s.i.

This procedure gives a final, compacted, unitary article of very greatdensity without requiring the use of very high static forces. Densitiesof refractory articles such as refractory bricks can be achieved by thisapparatus and process which are greater than that which can be achievedwith only static forces and presently existing apparatus for applyingsuch static forces. Existing apparatus such as conventional brickpresses can be modi fied in a manner similar to that shown in thedrawing to practice this invention.

It should be understood that the hydraulic cylinders 4 and 7 serve thefunction of positioning and that this function could be accomplished byother means, also that more than one actuator can be employed in asingle press and that one or more servo valves (depending on the natureof the valve) can be employed with each actuator. For example, anactuator with one or more servo valves can be interposed betweencrosshead 9 and die 13 in the same manner shown for crosshead 6 and die15 in the drawing. In this manner both dies 13 and 15 will carry thestatic force with the superimposed cyclic force. In the operation ofthis apparatus the cyclic forces can be applied to dies 15 and 13 inphase or up to out of phase as desired by merely controlling theelectrical signals to the various servo valves. Similarly, more than oneactuator can be employed between a given die and its supportingcrosshead.

It should also be noted that the static force and/or the dynamic forceor forces imposed on a given die can be varied during the compactionprocess. For example, light static loads can be applied at the initialcompaction stage which, as noted above, is mostly taken up byaccommodation of the particles in relation to adjacent particles. Thestatic load can then be increased at the final stage of compaction whereparticle fracturing is necessary for further densification. Similarly,while varying the static force from one stage in the compactionprocedure to the next, the cyclic force and/ or its frequency can bevaried from one stage of the compaction procedure to the next. Forexample, the frequency of the compaction force in the initial stage ofaccommodation and secondary stage of elastic and/or plastic deformationof the particles can be low, e.g., 100 cycles per second, and thenincreased to, for example, 2,000 cycles per second during the finalstage when compaction is achieved primarily by fracturing of theparticles under the increased static force. Other variations andcombinations of the static and cycling forces as well as other processparameters such as frequency are obvious to those skilled in the art andtherefore will not be discussed in detail.

In the process of this invention a particulate material is compacted ina molding zone with at least one die, at least one of the dies havingimposed thereon a static compressive force which is transmitted to theparticulate material and a superimposed additional force which iscyclically applied in the range from about 0.2 to about 7,000 cycles persecond. The static force is a finite force up to about 40,000 pounds persquare inch of die area while the cyclic force is a finite force up toabout 2,000 pounds per square inch of die area, both die areas being asdefined above.

The process of this invention is applicable to any particulate materialsuch as fireclay, alumina, mullite, corundum, magnesite, chrome ore,silica, zircon, zirconia, carbon, kaolin, and the like; subdividedmetals normally used in powder metallurgy processes such as aluminum,beryllium and its alloys, copper, brass, bronze, iron, lead, magnesium,titanium, zinc, zirconium and its alloys, and the like. This inventionis applicable to other subdivided materials such as ground glass,comminuted plastic, woodchips, carbon black, rubber particles, shreadedpaper, and the like. Mixtures of two or more of the above materials canbe employed if desired.

EXAMPLE In the apparatus of the drawing, magnesite brick mix consistingof a gradation of sizes ranging from 100 percent through 4 mesh to 25percent through 325 mesh screen (Tyler) is charged into cavity 12 anddie 15 moved downwardly just into contact with the upper surface of themagnesite particles in the cavity. A hydraulic pressure of 700 p.s.i. isapplied through conduit 31 in chamber 28 which produces a static forceof 125,000 pounds at die 15. Die 15 has an area in contact with themagnesite particles of 20 square inches and therefore a static force of6,250 pounds per square inch is applied to the magnesite particles.

Hydraulic pressure of 3,000 pounds per square inch is cyclically appliedthrough conduits 32 and 33 thereby resulting in a cyclic force of or15,000 pounds (750 p.s.i.) at die 15. The cyclic force is applied at afrequency of 2,000 cycles per second using a hydraulic flow throughservo valve 17 of about 3 gallons per minute.

After about 3 seconds the static and cyclic forces are terminated, die15 removed from cavity 12 and die 13 raised further by piston 8 to raisethe compacted magnesite brick from the interior of cavity 12 to theupper surface of mold for removal from the apparatus.

Reasonable variations and modifications are possible Within the scope ofthis disclosure without departing from the spirit and scope of thisinvention.

The embodiments of the invention in which an ex clusive property orprivilege is claimed are defined as follows:

1. In apparatus for compressing particulate material in a molding cavityhaving an upper die and a lower die which enter the cavity opposing oneanother, thereby defining upper and lower cavity surfaces, theimprovement comprising:

at least one actuator means operably connected to at least one die forforcing said die toward and away from. said cavity,

each actuator means having operatively connected thereto two servo valvemeans, to cause said actuator means to apply to a die both a staticforce toward said cavity and a reciprocatnig force toward and away fromsaid cavity, and

means for controlling said servo valve means.

2. The apparatus according to claim 1 wherein said actuator meanscomprises a body having a first piston chamber therein and a secondpiston chamber opening directly into said first chamber, said bodyhaving an opening into said first chamber to allow a piston to passthrough said opening into said first chamber, said opening being asmaller cross-sectional area than said first chamber, a first pistonmeans extending through said opening into said first chamber, said firstpiston being of substantially the same cross-sectional area as saidopening and having an annular flange on a portion thereof in theinterior of said first chamber, said flange extending out to theinterior walls of said first chamber thereby dividing said first chamberinto two sub-chambers, second piston means carried by said first pistonmeans and extending into said second chamber, conduit means in said bodyopenly communicating with said second chamber and each of saidsub-chambers in said first chambers, said conduit means being openlyconnected to said servo valve means.

3. The apparatus according to claim 2 wherein said servo valve means isan electrically actuated means which hydraulically operates saidactuator means.

References Cited UNITED STATES PATENTS 2,549,642 4/1951 Seelig 2541 I X2,569,226 9/1951 Carter 2541 I UX 2,747,231 5/1956 Reinhardt l816 R UX3,129,463 4/1964 Gill, Jr. et al. 25-41 I X 3,423,794 1/1969 Wilsonl816.5

OTHER REFERENCES American Ceramic Society Journal, Vibratory Compactingof Metal and Ceramic Powders," by William C. Bell et al., vol. 38, No.11, November 1955, pp. 396-404.

WILLIAM s. LAWSON, Primary Examiner U.S. Cl. X.R.

Iii-DIG 28

